The CDC and APHIS have issued proposed rule to amend and republish the list of select agents and toxins that have the potential to pose a severe threat to animal or plant health, or to animal or plant products. The proposed rule would also reorganize the list of select agents and toxins based on the relative potential of each select agent or toxin to be misused to adversely affect human, plant, or animal health. Such tiering of the list would allow for the optimization of security measures for those select agents or toxins that present the greatest risk of deliberate misuse with the most significant potential for mass casualties or devastating effects to the economy, critical infrastructure, or public confidence.